1. Field of the Invention
The present invention relates to a high-frequency module including a plurality of filter elements.
2. Description of the Related Art
In mobile devices and the like having wireless communication functions, a filter circuit is used to allow only a high-frequency signal at a desired frequency to pass and attenuate high-frequency signals at frequencies aside from the desired frequency.
For example, Japanese Unexamined Patent Application Publication No. 2012-109818 discloses a filter circuit including a plurality of SAW (surface acoustic wave) filters. Specifically, in the filter circuit according to Japanese Unexamined Patent Application Publication No. 2012-109818, the plurality of SAW filters are connected in series between an input terminal and an output terminal. SAW filters are also connected between connection lines that connect the SAW filters connected in series and grounds.
The filter circuit disclosed in Japanese Unexamined Patent Application Publication No. 2012-109818 includes an inductor or a series circuit constituted of an inductor and a capacitor (called a correction circuit) connected in parallel to the SAW filter series circuit in order to improve attenuation characteristics outside of the pass band. At this time, the correction circuit is adjusted so that a high-frequency signal outside of the pass band (a suppression target signal) propagating in a circuit section constituted by the SAW filter group and the suppression target signal propagating in the correction circuit have the same amplitude and inverted phases against each other. As a result, the suppression target signals cancel each other out at a connection point between the circuit section constituted by the SAW filter group and the correction circuit and are not outputted from the output terminal.
However, in the above-described structure, it is necessary to provide the correction circuit, including an inductor or a series circuit constituted of an inductor and a capacitor, simply to improve the attenuation characteristics, in addition to the circuit section constituted of the SAW filter group providing the main filter function.
This increases the number of constituent elements in the filter circuit and thus increases the size of the filter circuit, and is therefore unsuitable for current mobile terminals and the like, which require increased miniaturization.